Television system



y 1935- I H. M. DOWSETT 2,002,937

' TELEVISION SYSTEM Filed y 2 1952 2 Sheets- Sheet 1 INVENTOR HARRY, M. DOWSETT ATTORNEY May 28, 1935. H, M. DOWSETTV' 3 I TELEVISION SYSTEM v 1 I Filed July 25, '1932 1 2 Sheets-Sheet 2 INVENTOR I HARRY M. D SETT ATTORNEY BY m'VL/ Patented May 28," 1935 V This invention relates to television systems and more particularly to television receivers.

The invention has for its object to provide'a television system wherein flicker in the received or reproduced picture shall be reduced or eliminated, wherein definition shall be improved, and wherein the general finish of the picture shall be improved. I L

In known television receivers employing scanning apparatus of the kind in which a spot of light is caused to traverse the received picture area,, or'in which picture elements are illuminated to reproduce a received picture, the intensity of any particular point on'the, picture at any particular instant is judgedby the eye with reierenceto and by compasion withthe intensity of a previous point or points reproduced during 7 the period of time; corresponding to the periodot persistence of vision. g-

To put the matter in. another way, the eye makes comparison with each point of thepicture with a point which has been produced before the particular point being considered.

According to this invention, means are provided for creating what may be termed a light frame orgrid or. reference so that the intensity of illumination of any point in the received picture may be appreciated by the observer not with reference to a previous point-in'the picture, but with reference to some point in the grid or frame which is provided for this purpose.

In one wayof carrying outthis invention, a grid of light having the same mesh as the number of picture points or elements in the received.

television picture is superposed on the said received picture onjthe. receivingscreen, so that in effect the modulated light of each point in the received picture is set in or against a thin square of light which serves as a background for comparison. In the casein which the picture is built of separate picture elements, the grid is arranged to lie as accurately as possibleron the dividing lines between the elements. in'which the received picture is built up by a traversed point of light, i. e., in which the received picture is built up in strips, the grid will .in effect divide each strip transversely into the equivalent number of elements, the projection being such that the grid lines also lie on the lines of junction of the strips.

The-light grid may be produced in any convenient manner, for example, by means of a lantern slide consisting 'of a, transparent grid of the required dimensions on aopaque or black background. For direct comparison light from TELEVISION sys'rnM Harry MelvilleDowsett, Winchniore Hill, London, England, assignor to Radio Corporation of- I 1 America, a corporation of Delaware Application July 25, 1932, Seria1No. 624,437 In Great Britain July 27, 1931 '4 Claims. (ol ve-6y direction opposite to the modulation of;the picfure;-

In the case I aw PAT T" asteady source may be employed'gandmay-be regulated to be about thesameintensitypmthe screen as that of thepioture byumnodulated light.

If' desired, the light grid may-itself be moduw lated in a direction opposite to. the picture modu-.; lation instead of being of constant intensity; Any known means may 'beemployed for; this pur g p 1: 2

In such an arrangement-the relative intensity; on any picture elementas judged bythe eye will, assuming the modulation of the gridto-be quantitatively equal to the modulation ofgthe picture; be twice as great as wouldbethecaseif, the; light in'the grid were unm dulated.--v 5y:

.In cases where it is difiicult or -inadvisable; to; employ a full grid,as above described, substant'al benefit may be obtained by employingmerel a frame of light for servingiasa baseofgc mpariS n, for the eye, i. e., the picture may be simplyjramed in a square of light ,which may, be either. a constant intensity or fmay-be modulated}:

elements. Again, in place of using a simple frame of light or a full grid substantial: advantagezmay I be obtained by providing a background garran-getment wherein four points of light around 'ach; picture element'are provided.;'-- 1 The invention is illustrated ;and;. furthe1- .ad scribed with reference to the acc.o ripanying; schematic drawings wherein; Figure; l;-;shows, ,in.

area when scanned schematic front view, part of a televisiomreceiverw i h may. be pl yedin one wavoi a ry n out the invention, whileFigureZ showsschernat ically a side view of the screen of Figure 1 Figure 3 illustrates another anne pt arryi -the invention into practice. Figure 4 is a view of a complete receiver. 7 V

Referring to Figures 1 and 2, in the methodcarrying out the invention therein illustrated a television image is built up andpresented toa large number of people by means of.-a number of signal lamps I which are viewed through a' ground glass or similar screen 2, the audience r 1 viewing the screen in the direction of the arrow shown in Figure 2. f

In accordance with the present invention small 1 A lamps 3 are placed between the signal lamps I as shown, and these small lamps 3 are maintained at a constant light intensity corresponding to the mean of the light intensity of the picture elements as reproduced by the signal lamps I. The

method of building 'up a received televisionpicture by means of signal lamps, such as the lamps I, is, per se, well known, and suggested, for ex-' ample, by United States Patent #1,673,828 and British Patent No. 222,604 and it is not thought necessary therefore to describe it in the present specification. To put the matter in another way, the arrangement shown in Figures 1 and 2 is a known arrangement except for the provision of the small lamps 3 which constitute a light frame or gridof reference. a

In the'method' of carrying out the invention illustrated in schematic perspective in Figure 3,,

a television screen 4 composed of translucent material is provided and is viewed in the direction of the arrow shown in Figure 3. The television picture elements, i. e., the elements which together constitute the received viewed television picture,

are projected on to the screen 4 by means of a light grid thrown'on the rearface of the translucent screen 41);? means of the lantern andlantern slide, formsanetw'ork 'of lines of constant intensity and thisintens'ity is chosen at the mean of the intensity of the modulated picture ele- 5 ments. 'I'hese'picture elements are schematically represented at "L i In a further modification (not illustrated) both the light grid and the modulated picture elements are'projected from the same side of the'screen on $170 the said screen,;which may. be viewed either by reason of light reflected therefrom; or'by light projected therethrough. 'In o'ther words; the arrangement of Figure 3-may be modified by locat in: the parts 6 and'5 both'ongthe same side of the'screen l;

It be seen that the present invention provides theadvantage, inter alia,that irregularities inscarmlng alignmentwill; to a great extent, be masked? A? complete diagrammatic sketch of a television -receiverand projector utilizing the form of screen shown infFigs. land 2'is shown-in Fig.4. I2 is the television receiver which passes the synchronizing impulsesalong the wires I l to the synchronous motor l0. This motor drives the commutator arms I and I3 thereby allowing television; signals tc-flo'w to the correct signal'lamps' I: ofthe screen l ythroughthe'slip rings 9, the commutator; segments 8 and the connecting wiresi.

' lamps 1': are kept' lighted at a constant 111- 6 represents a tensity by means of the battery or source of Having now described my invention, what I claim and desire to secure by Letters Patent is the following:

1. In television receiving apparatus, a viewing panel on which electro-optical image reproductions are to be made, means forproducing over the several elemental areas of the viewing panel signal controlled point representations of thevarying values of lights and shadows of a subject of which the electro-optical image is being produced, and a plurality of light producing means surrounding each point of controlled light representation for producing independently of signalling indications constant intensity illumination over areas surrounding the areas of image point representations.

2. 'Intelevision receiving apparatus, a viewingarea, means for producing on the viewing area a sequenceiof light points of varying intensities of lights and shadows controlled-in accordance with the areas of controlled intensity light representations.

3 In television apparatus, a plurality of light sources arranged with loci corresponding to the several elemental areas into which a subject of which the electro-optical image is desired is assumed to-be divided for image transmission purposes, means for energizing the several light sources successively to causeillumination thereof alonga" series of paths substantially parallel, a plurality of independent light sources arranged adjacent-each of the first named light sources, and meansfor illuminating the last named light source's from a' local source to a constant intensity illumination. 9

4. In television receiving apparatus, a plurality of light producing elements for recompo sing'a viewed television image, a second plurality of light producing elements interposed between each of the first named light producing elements, means for receiving television signals, means for controllingthe intensity of light on successive light producing elements of the'first named plurality inaccordance with the-received signals, and means forilluminating the second plurality of light producing elements from a local source.

-HARRY MELVILLE DOWSE'I'I. 

